Use blue tack, now in many colors.
Otherwise there's the china type transparent silicon double side tape with red sticker cover (non washable) from hardware shop. You wont find it in ace, have to be hardware shop.. in ace only got gorilla brand. I guess it works too but expensive.
Looks like this

https://s.lazada.com.my/s.4qYeT

Looks like the same one. Unless yours is the washable kind . The non washable is stronger.
But since you stick st the aide (versus a tweeter holder that sits on the dash), its very hard bro
Time to mod your A pillar.
Sorry not much help. Maybe Gorilla tape?